if you wait, there will always be something better out, especially in the mobile market.
Now with the Bold and the newer BB's coming (javelin, thunder/storm/kickstart) and rim showing more interest in the typical consumer market it does look like they will be releasing more and more phones on a regular basis. They will have to if they want to grow at the end of the day, because other manufacturers tend to release new models on a monthly basis. Then you also take the fact that 3G penetration is growing quite rapidly in the states and canada, so now other manufacturers will be releasing a lot of phones there that in the past they never would have bothered to. Another reason why Rim will need to pick up the pace to ward off new competition they never had before on their home turf.
I think blackberry users have become used to the fact that previously it took so long for rim to release a new device, so people were ok with keeping what they have for a while, which is not the norm in a lot of places. This will definitely change and if you can afford it, you will be upgrading everytime somehting you fancy comes out.
8900 Curve, IPHONE 3G, SAMSUNG JET, NOKIA E71, BOLD, STORM 9500